Escherichia coli are common members of the enteric community in a broad range of mammals. Although most E.coli are non-pathogenic, a small subpopulation, including but not limited to serotype O157:H7, demonstrates virulence factors such as attachment genes, hemolysin production and shiga-like toxins. Symptoms of pathogenic infection in humans range from mild diarrhea to hemolytic uremic syndrome. Ruminants constitute the primary reservoir of the O157:H7 serotype, and unlike humans, these animals are not negatively affected by the bacteria. Up to 30% of the animals within some beef herds have been shown to shed these bacteria at any given time, but not all ruminants are carriers and much lies undiscovered regarding the ecology of these human pathogens. The general purpose of this study was to gain understanding of growth kinetics of serotype O157:H7 and commensal E. coli by examining their activities in diverse sets of interactions. Ultimately, the goal was to discover whether commensal E. coli and serotype O157:H7 compete for the name nutrient-niche to ascertain whether competitive exclusion would be a viable method of pathogenic mitigation. Approximately, 1000 isolates were obtained from the feces of a local herd of beef cattle in Nappan, Nova-Scotia and then typed by REP-PCR and PFGE. Growth kinetics for monocultures were then determined for all representative pulsotypes along with a panel of 50 unique O157:H7 isolates using impedance technology (RABIT). Previous studies examined few isolates of E. coli at a time : however, this study is novel as it incorporates a large number of serotype O157:H7 and commensal E. coli isolates in growth characterizing assays. All pulsotypes were then tested for presence of colicin, phage, and virulence factors. Growth dynamics were measured by competition of commensal and O157:H7 strains by combining impedance technology with end-point enumerations on BCIG agar. Growth rates differed significantly between commensal strains and O157:H7 serotypes. Certain strains metabolize different nutrients at different rates, so three nutrient supplements were tested in the impedance system to shed light on their conference of advantage in a competitive system. Further testing of substrate impact on competition is required.

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